The present invention relates to the field of planar or flat panel displays. A variety of technologies have been proposed for such flat panel light emitting diode arrays, electroluminescent arrays, and liquid crystal arrays. The addressing systems have included coincidence X-Y addressing, and more recently the use of thin film transistor control circuitry integral on the panel with individual display elements as seen in U.S. Pat. Nos. 3,840,695 and 4,006,383.
The thin film transistor provides an electrical device uniquely suitable for use in flat panel display devices. It is known that a thin film transistor can be fabricated with an insulated floating gate to provide a device with controllable variable conductance properties, which can be termed a memory transistor. Such devices and fabrication techniques are set forth in "Experimental Realization of Floating-Gate-Memory Thin-Film Transistor", Proceedings of the IEEE, Vol. 63, pp. 826-827, May 1975.
The liquid crystal display medium is a passive rather than active medium and for this reason offers several important functional advantages. These include the ability to utilize ambient light and to be readable in high external light level conditions. The medium can be driven by low DC voltage and are low power consumption devices. A liquid crystal display can be based on controlled light transmissivity or reflectivity.
The thin film memory transistor integrally combined with the liquid crystal display medium eliminates the need for large area signal storage capacitors as part of the display element, thus optimizing the liquid crystal medium area. The transistor provides the necessary threshold and elemental storage needed for refresh multiplexing applications. The liquid crystal medium can be of the twisted nematic or dynamic scattering operating mode.
The electro-optic display system of the present invention can be used to display alpha-numeric information as well as to provide a general pictoral display.